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How to adjust input sensitivity on a car audio amplifier.

Many people have asked me what is the correct way to adjust the input sensitivity on a car audio amplifier. The right way is with an Oscilloscope (often referred to as O-scope) but that's an expensive piece of equipment. Plus, if they have that then they already know how to use it. This page instead will focus on the second best method of using a Digital Multi-Meter (DMM) capable of reading AC Voltage.

What you need:
  1. A CD (or other playable high-quality media) containing non-attenuated test tones (0dB reference level) in the frequency range of the intended device. 40-80Hz for most subs and 500-2000Hz for fill speakers for example.
  2. A Digital Multi-Meter (DMM) capable of reading AC Voltage (Vrms).
  3. A simple calculator (or the form on this page).
What to do:
  1. Figure out the Vrms to watch for with the Voltmeter using the following formula:
    Vrms = Square_Root(Expected_Amp_Power_RMS * As-Wired_Impedance)
    Expected Amp Output (RMS):   As-Wired Impedance:  
  2. Make or get the CD with the test tones. Here are some you can use:
  3. Disconnect the speakers from the amp if they are already connected.
  4. Turn off all signal boosting, enhancing, or processing options on all equipment. (I.E. Loudness, bass boost, etc..)
  5. Set any bass/treble or eq controls to middle or flat (0dB settings).
  6. Set the volume on the head unit to just below it's clipping state or 3/4 of full volume if exact clipping state is not known.
  7. If the head unit has an option for specific channel control and it's not centered on 0dB, set it to 3/4 it's rated capability.
  8. Set the input sensativity to the minimum setting.
  9. Connect the Voltmeter to the amp as the speakers would be wired.
  10. Play the corresponding test tone for the speakers you will be using.
  11. Adjust the input sensitivity until the voltage reads the expected output.
  12. Reattach the speakers.
Now you have the maximum unclipped setting for the amp as you plan to wire it. (maybe mark it with something for reference) From this point you can lower it again for system balance if desired but do not go above this point.

Notices:
TOOLS:
Calculate Impedance

All Content Copywright 2003-2006 Christopher Stiefel. All Rights Reserved.
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